Method of drilling wells



Patented July 28, 1959 2,896,915 METHOD OF DRILLING WELLS Walter J.Weiss, Sugar Land, and Richard H. Graves and Wilbur L. Hall, Bellaire,Tex., assignors to The Texas Company, New York, N.Y., a corporation ofDelaware No Drawing. Application April 12, 1957 Serial No. 652,369 4Claims. (Cl. 2551.8)

This invention relates to the drilling of wells through subsurfaceformations by means of well drilling tools. More particularly, thisinvention relates to a drilling operation, such as a rotary drillingoperation, which involves circulation of a drilling fluid through thewell bore and about the drilling bit. In a rotary drilling operation adrilling fluid is pumped down the drill stem to the drilling bit at thebottom of the bore hole. The stream of drilling fluid then passesthrough the drilling bit and moves upwardly through the annular spacebetween the drill stem and the well bore wall carrying With it thedrilling cuttings.

In some areas, such as in the-area of the Gulf Coast of Texas andLouisiana, formations known as heaving or sloughing shales arepenetrated during a well drilling operation. The penetration of theseformations while employing conventional aqueous or water-base drillingfluids has been difficult due to the mud making characteristics orproperties of heaving shales. These shales have a tendency todisintegrate by swelling or cracking upon contact with Water with theresult that the walls of the bore hole become unstable or incompetentand the heaving shale material making up the walls of the bore holebecomes unstable and sloughs into the bore hole. In some instances thesloughing or moving of this heaving shale material into the bone holeresults in a stuck drill stem. In other instances the heaving shalematerial swells and sloughs or caves into the bore hole with a resultingenlargement of the bore hole and the formation of large subterraneancavities.

In addition to the above-indicated difficulties of maintaining a truebore hole when drilling through heaving shale material with aconventional water-base mud, the resulting finely dispersed heavingshale material taken up into the drilling fluid, because of the mudmaking properties of heaving shale, adversely affects the viscositycharacteristics of the drilling fluid. Upon a continued accumulation ofthese finely divided heaving shale particles in the drilling fluid theviscosity of the drilling fluid increases with the result that thedrilling fluid must be thinned by the addition of costly chemicalsthereto or by dilution with water. If the drilling fluid is thinned bywater dilution the addition of more weighting material such as bariumsulfate (barytes), iron oxide, lead sulfide (galena) and the like isnecessary to maintain a given mud weight.

Special drilling fluids or muds have been developed for drilling throughheaving shale formations. One such drilling fluid which has beenemployed for drilling through heaving shale formations is a drillingfluid containing aqueous sodium silicate. Another drilling fluid whichhas been proposed for use during a drilling operation while drillingthrough less seriously dispersing or heaving shale formations is a highpH lime-base drilling fluid which contains lime together with quebracho,caustic soda, water and the conventional hydratable bentonitic type ofdrilling clay. High pH, lime-base drilling fluids, however, cannot beemployed without considerable difliculty while drilling through the moreseriously heaving shale formatitiii si Additionally, a high pH,lime-base drilling fluid is sensitive to salt contamination, such ascontamination by calcium chloride or calcium sulfate,

which causes clay flocculation with a resulting increase in viscosityand water loss. Although in some instances the desirable viscosity, mudweight and water loss properties of a high pH, lime-base drilling mudcan be maintained while drilling through a heaving shale formation bythe addition of suitable additives, such as the addition of caustic sodaand a quebracho and the like, the continued addition of these additivesto the drilling fluid usually involves considerable expense.

In copending, coassigned patent application Serial No. 596,456, filedJuly 9, 1956, now US. 2,802,783, there is described an aqueous orwater-base drilling fluid particularly suitable for drilling throughheaving shale formations. Thedisclosures of this application are hereinincorporated and made a part of this disclosure. The aforesaididentified patent application describes this drilling fluid as beingcharacterized by a relatively high dissolved calcium or calcium ioncontent suflicient to effectively stabilize and control the mud makingproperties of heaving shale material or clays in contact with thedrilling fluid described therein. The particular drilling fluiddescribed therein is characterized by a relatively high dissolvedcalcium or calcium ion content suflicient to effectively stabilize andcontrol the mud making properties of heaving shale material or clays incontact therewith. More particularly, the drilling fluid describedtherein is characterized as an aqueous drilling fluid comprising analkaline aqueous phase (filtrate phase) which is saturated with re-.

spect to calcium hydroxide and which contains a Water soluble calciumsalt which has a solubility in said aqueous phase greater than that ofcalcium hydroxide dissolved therein in an amount sufficient to yield acalcium or calcium ion concentration in said aqueous phase of at least200 parts per million by weight. that any water soluble calcium salt maybe employed in the preparation of such a drilling fluid provided thecalcium salt is more soluble in water, e.g., as measured at roomtemperature of about 25 C., than calcium hydroxide Ca(OH) and providedthe calcium salt when added to water produces or generates the desiredfree calcium or calcium ion content therein. Satisfactory Water solublecalcium salts which may be employed in the preparation of such drillingfluids include calcium chloride CaCl calcium sulfate CaSO calciumacetate Ca(C H O calcium formate Ca(CHO calcium nitrate Ca(NO calciumgluconate Oa(CH OH(CHOH) .COO)

Other Water soluble calcium salts might also be employed.

As disclosed in the foregoing patent application the calcium hydroxidepresent in the aqueous, phase of the particular aqueous drilling fluiddescribed therein may be added directly to the drilling fluid ashydrated lime soluble alkali metal base such as sodium hydroxide, the,

various ingredients being added in an amount sufficient to at leastgenerate the amount of calcium hydroxide required to saturate theaqueous phase of the drilling fluid.

It is an object of this invention to provide a drilling method employingthe above-identified drilling fluids whereby optimum results might beobtained in a drilling j operation.

Still another object of this invention is to provide, an improved.drilling method for drilling through heaving shale formations.

Yet another object of this invention is-to provide. an

improved drilling fluid particularly suitable for drilling I throughheaving shale formations and the like.

This application discloses.

In accordance'with this invention an improved drilling fluidparticularly" suitable for drilling through, heaving shaldformatiohs isobtained byproviding an aqueous drilling fluid comprising a hydratableclayey material weightgsaid aqueous phase having a pH not greaterthan12.6 and a numerical value of 'M /P not greater than-a numerical valueselected from the group consisting of, 3.0

and 5.0,"said numerical value being not'greater'than 3.0

when said dissolved calcium or calcium salt dissolved in said aqueousphase is derived from or is an inorganic calcium salt and said numericalvalue being not greater than 5.0 when said dissolved calicum orcalcium'salt dissolved in'said aqueous phase is derived from or is anorganic calcium salt wherein M; is the number of ccs'. of N/SO H 80required to titrate 1 cc. of said aqueous phase to methyl orangeendpoint and his the number of ccs. of

N/SO H 80 required to titrate 1- cc. of said aqueous phase tophenolphthalein end point.

In a drilling operation it has been observed that an improved drillingoperation is obtained and mud making during the drilling operation whenpenetrating certain shale formations is substantially reduced, asevidenced by a reduced amount of weighting material being requiredduring the drilling operation to maintain a given mud weight, bymaintaining the M ll, value of'the aboveidentified mud with the rangesindicated. In the case.

wherein the calcium salt added or present in the aqueous filtrate. phaseof the drilling mud is an inorganic calcium salt, such as calciumchloride, the'M /P, value should not be greater than 3.0, preferably 2.0or less. On the other hand, when the aqueous filtrate phase of thedrilling mud has added thereto or contains therein the equivalent of awater soluble organic calicum salt, such as calcium acetate; thenumerical value of M P, should be less than 5.0.

A typical unweighted drilling mud containing hydratable drilling clayand 1 /2 lbs. of calcium chloride per barrel of drilling fluid, 3 lbs.of calcium lignosulfonate (Kembreak, clay dispersing agent) per barrelof drilling fluid and 3 lbs; of lime per barrel of drilling fluid mightexihibt the following properties:

barrel of drilling fluid. Calcium-ion content About 400 p.p.m. asdetermined by the standard Versenate method described in API Code RP-29.pH Not greater than 12.6, in the range 11.2-12.5. Water loss About 8cos. after the addition of about 4 lbs. of starch per barreldrillingfluid.

Asindicated in' the above-identified patent applications any'suitabledispersing agent may be employed in the preparation of a drilling fluidin accordance with this iiivention provided it is compatiblewith itsenvironment in the drilling mud, i.e., is not salted out and does notundergo a chemical or physical change, which would render it unsuitableoruseless as a dispersing agent and provided it exhibits sufiicientdispersing power in the drilling mud to disperse the hydratabledrilling'clay material vw ithin the drilling mud. A'n especiallysatisfactory dispersant-is a lignosulfonate such as an alkali metalor-an I alkaline earth metal lignosulfonate, especially lignosulfonatessuch as calcium lignosulfonate derived from soft woods by theMarathon-Howard process. Suitable dispersing agents aresodiumlignosulfonates and calcium lignosulfonates. Commerciallyavailable calcium lignosulfonates such as Kembreak and Lignox areparticularly satisfactory. Other suitable dispersing agents includeyellow dextrin, a degradation product of starch, Q-Broxin, aferro-chrome-containing lignosulfonate, Rayflo, a predominantly sodiumsalt of a polymeric'polyphenol derivative apparently obtained as anextract of hemlock bark.

The drillingfluids in accordance with this invention may alsoinclude'the usual drilling fluid additives such .as' water lossadditives, e.g., Impermex or My-lo-gel, preh'ydrolyzed' starch products,,CMC, a carboxymethylceltion of low density solids in the drillingfluid. This accumulation of mud solids in the drilling fluid requiresthat the drilling fluid often be diluted with water in order I .tomaintain 'a satisfactoryclay-Water relationship.

With drilling fluids of this invention the necessity to maintain a highdensity drilling fluid by the continual adjustment of the clay-waterrelationship by the addition of water and weighting material to thedrilling fluid is avoided, by maintaining the value M /P; of thedrilling fluid ina range in accordance with the teachings of thisinvention. Further, by utilizing the teachings of this inventionaniniproved drilling operation is obtainable.

The following is exemplary of the practice of this invention andindicates the advantage when employing an aqueous drilling fluid havingan alkaline aqueous filtrate phase saturatedwith respect to calciumhydroxide and containing. a calcium ion concentration greater than 200parts per million by weight, for example in the range 300-1000 parts permillion by weight, the pH of said filtrate phase being not greater than12.6, preferably in the range 11.2-12.5, ofmaintaining the M /P ratio ofthe drilling fluid at a value in accordance with the practice of thisinvention. In actual drilling operation wherein a conventional waterbase clay mud was converted to a shale control mud as describedhereinabove by the addition thereto of calcium chloride, calciumlignosulfonate (Kembreak), lime and starch in the amounts 1 /2, 3, 3 and4 lbs. per barrel of mud, respectively, it was observed during thedrilling operation, which in this instance employed an inorganic watersoluble calcium salt (calcium chloride), that when the M ,/P,: ratio waspermitted to reach a value greater than 3, although a certain amount ofshale control was exhibited, the ability of the drilling fluid to avoidmud making when a heaving shale or normally mud making formation wasencountered, was less than desirable. This wasexhibited by the fact thatwhen the M /P, ratio exceeded a value of 3 mud making occurred andrequired the addition of a very large excess of weighting agent over theamount theoretically required in order to maintain a given mud weight.The advantages of employing i1 {killing mud 'having a controlled M /Pratio The test data set forth in Table I was obtained during a drillingoperation wherein the shale formation was topped at a depth of 9,144feet and the shale control mud employed during the operation was anaqueous hole mud broken over by the addition of calcium chloride,Kembreak, lime and hydrolyzed starch in the amounts (#/bbl. mud) l, 3, 3and 4 respectively.

With respect to a shale control drilling mud in accordance with thepractice of this invention wherein a water soluble organic calcium saltsuch as calcium acetate is employed in the preparation thereof it hasbeen observed that a drilling mud prepared by adding to an aqueousLouisiana hole mud calcium acetate, Kenrbreak and lime in the amounts 1,3, 3 lbs. per barrel of mud the resulting drilling mud possessed thefollowing properties:

It was observed that the aqueous filtrate phase resulting from the aboveformulated mud was capable of hardening shale. On the other hand, adrilling mud prepared by the addition of calcium acetate, sodiumhydroxide and Kembreak in the amounts 2.38, 1.08 and 4 lbs. per barrelof mud, respectively, and another drilling mud prepared by the additionof sodium acetate tri'hydrate, lime and Kembreak in the amounts 1.84, 1,4 lbs. per barrel of mud, respectively, the muds having an Mj/Pf valueof 11.3 and 7.8, respectively, exhibited substantially no shalehardening properties but rather tended to disperse shale therein andtherefore possessed mud making properties.

The data set forth in Table I hereinabove clearly indicates theadvantages, as evidenced by a reduced requirement of weighting agent tomaintain a given mud weight, of maintaining M /P, at a value inaccordance with this invention. If the value of M f/Pf exceeds thatpreferred in the practice of this invention the M f/Pj can be adjustedby adding to the mud an amount of lime or calcium hydroxide or causticsoda sufficient to reduce M f/Pf to a suitable value, preferably lessthan 2.0. It is preferred to adjust M /P; to a suitable value by the useof an alkali metal hydroxide such as NaOH which by reaction with calciumions in the filtrate phase generates calcium hydroxide in situ. Itappears that in situ generated calcium hydroxide is more effective inaltering and/or maintaining Mj/P] at a value in the desired range.

As will be apparent to those skilled in the art in the light of theforegoing disclosure many substitutions, a1- terations and changes arepossible in the practice of this invention without departing from thespirit or scope thereof.

We claim:

1. In the drilling of a bore hole through a heaving shale formationwherein an aqueous drilling fluid is passed through the bore hole duringthe drilling operation and wherein the drilling fluid comprises ahydratable clayey material dispersed in an alkaline aqueous filtratephase and a dispersing agent for said clayey material therein, saidaqueous phase consisting essentially of a saturated aqueous calciumhydroxide solution and a water soluble calcium salt which has asolubility in said aqueous phase greater than that of calcium hydroxidedissolved therein to yield a calcium ion concentration in said aqueousphase of at least 200 parts per million by weight, said aqueous phasehaving a pH not greater than 12.6 and wherein during the drillingoperation the numerical value of M /P of the drilling fluid tends toexceed 3.0 when said calcium salt dissolved in said aqueous phase is aninorganic calcium salt and 5.0 when said calcium salt dissolved in saidaqueous phase is an organic calcium salt, M being the number of cos. ofN/SO H 50 required to titrate 1 cc. of said aqueous phase to methylorange end point and P being the number of cos. of N/SO H required totitrate 1 cc. of said aqueous phase to phenolphthalein end point, theimprovement which comprises maintaining said aqueous phase saturatedwith calcium hydroxide and adjusting the M ,/P, value of the drillingfluid when the value exceeds 3.0 to a value below 3.0 when said calciumsalt is an inorganic salt and when the value exceeds 5.0 to a valuebelow 5.0 when said calcium salt is an organic calcium salt by adding tosaid drilling fluid a suitable amount of an alkaline material selectedfrom the group consisting of lime and an alkali metal hydroxide.

2. A method in accordance with claim 1 wherein said calcium ionconcentration is in the range 300l000 parts per million by weight.

3. A method in accordance with claim 1 wherein said calcium salt is aninorganic calcium salt selected from the group consisting of calciumchloride, calcium sulfate and calcium nitrate and wherein the numericalvalue of M /P; is adjusted to a value not greater than 2.0.

4. In the drilling of a bore hole through a heaving shale formationwherein an aqueous drilling fluid is passed through the bore hole duringthe drilling operation and wherein the drilling fluid comprises ahydratable clayey material dispersed in an alkaline aqueous filtratephase and a dispersing agent forsaid clayey material therein, saidaqueous phase consisting essentially of a saturated aqueous calciumhydroxide solution and a water soluble calcium salt which has asolubility in said aqueous phase greater than that of calcium hydroxidedissolved therein to yield a calcium ion concentration in said aqueousphase of at least 200 parts per million by weight, said aqueous phasehaving a pH not greater than 12.6 and wherein during the drillingoperation the numerical value of M ;/P 'of the drilling fluid tends toexceed 3.0 when said calcium salt dissolved in said aqueous phase is aninorganic calcium salt and 5.0 when said calcium salt dissolved in saidaqueous phase is an organic calcium salt, Mg being the number of cos. ofN/50 H 80 required to titrate 1 cc. of said aqueous phase to methylorange end point and P being the number of cos. of N/SO H 50 required totitrate 1 cc. of said aqueous phase to phenolphthalein end point, theimprovement which comprises maintaining said aqueous phase saturatedwith calcium hydroxide and adjusting the M;/P; value of the drillingfluid when the value exceeds 3.0 to a value below 3.0 when said calciumsalt is an inorganic salt and when the value exceeds 5.0 to a valuebelow 5.0 when said calcium salt is an organic calcium salt by adding tosaid drilling fluid a suitable amount of an alkali metal hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN THE DRILLING OF A BORE HOLE THROUGH A HEAVING SHALE FORMATIONWHEREIN AN AQUEOUS DRILLING FLUID IS PASSED THROUGH THE BORE HOLE DURINGTHE DRILLING OPERATION AND WHEREIN THE DRILLING FLUID COMPRISES AHYDRATABLE CLAYEY MATERIAL DISPERSED IN AN ALKALINE AQUEOUS FILTRATEPHASE AND A DISPERSING AGENT FOR SAID CLAYEY MATERIAL THEREIN, SAIDAQUEOUS PHASE CONSISTING ESSENTIALLY OF A SATURATED AQUEOUS CALCIUMHYDROXIDE SOLUTION AND A WATER SOLUBLE CALCIUM SALT WHICH HAS ASOLUBILITY IN SAID AQUEOUS PHASE GREATER THAN THAT OF CALCIUM HYDROXIDEDISSOLVED THEREIN TO YIELD A CALCIUM ION CONCENTRATION IN SAID AQUEOUSPHASE OF AT LEAST 200 PARTS PER MILLION BY WEIGHT, SAID AQUEOUS PHASEHAVING A PH NOT GREATER THAN 12.6 AND WHEREIN DURING THE DRILLINGOPERATION THE NUMERICAL VALUE OF MF/PF OF THE DRILLING FLUID TENDS TOEXCEED 3.0 WHEN SAID CALCIUM SALT DISSOLVED IN SAID AQUEOUS PHASE IS ANINORGANIC CALCIUM SALT AND 5.0 WHEN SAID CALCIUM SALT DISSOLVED IN SAIDAQUEOUS PHASE IS AN ORGANIC CALCIUM SALT, MF BEING THE NUMBER OF CCS. OFN/50 H2SO4 REQUIRED TO TITRATE 1 CC. OF SAID AQUEOUS PHASE TO METHYLORANGE END POINT AND PF BEING THE NUMBER OF CCS. OF N/50 H2SO4 REQUIREDTO TITRATE 1 CC. OF SAID AQUEOUS PHASE TO PHENOLPHTHALEIN END POINT, THEIMPROVEMENT WHICH COMPRISES MAINTAINING SAID AQUEOUS PHASE SATURATEDWITH CALCIUM HYDROXIDE AND ADJUSTING THE MF/PF VALUE OF THE DRILLINGFLUID WHEN THE VALUE EXCEEDS 3.0 TO A VALUE BELOW 3.0 WHEN SAID CALCIUMSALT IS AN INORGANIC SALT AND WHEN THE VALUE EXCEEDS 5.0 TO A VALUEBELOW 5.0 WHEN SAID CALCIUM SALT IS AN ORGANIC CALCIUM SALT BY ADDING TOSAID DRILLING FLUID A SUITABLE AMOUNT OF AN ALKALINE MATERIAL SELECTEDFROM THE GROUP CONSISTING OF LIME AND AN ALKALI METAL HYDROXIDE.